The Containment for a device has BGP PeerState showing as SNMP_EXP_NOSUCHINSTANCE.
SMARTS - 10.1.x
This particular message means a particular index is not present in the MIB and hence the agent returns a NOSUCHINSTANCE error.
The issue was caused by configuration changes on the device. Deleting the device and rediscovering picks up the correct indexes and removes the message.